Methods for applying polyurethane coatings to golf balls having a thermoplastic polyurethane cover and resulting golf balls

ABSTRACT

Golf balls having covers made of thermoplastic polyurethane compositions are provided. Multi-piece golf balls can be made. Polyurethane primer coatings and polyurethane top-coatings are applied to the thermoplastic polyurethane cover. Different coating methods can be used. Isocyanate-rich and polyol-rich polyurethane coatings can be applied. In one embodiment, the golf ball can be treated with a multi-functional isocyanate prior to applying the coatings. The polyurethane cover composition and surface coatings can further include catalysts, ultraviolet (UV)-light stabilizers, and other additives. Heat is used to cure the coatings. The coating methods have many benefits and the finished balls have good physical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-assigned U.S. patent applicationSer. No. 15/710,866 filed on Sep. 21, 2017, now allowed, the entiredisclosure of which is incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention generally relates to golf balls having covers madeof thermoplastic polyurethane compositions. The golf ball includes aninner core and surrounding thermoplastic polyurethane outer cover.Multi-piece golf balls having outer cores, inner covers, andintermediate layers can be made. The invention includes methods forapplying polyurethane coatings to the thermoplastic polyurethane cover.The invention also encompasses the resulting balls. The finished ballswith thermoplastic polyurethane covers and surface polyurethane coatingshave many advantageous physical and playing performance properties.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. The inner core is made of a natural orsynthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

Three-piece, four-piece, and even five-piece balls have become morepopular over the years. More golfers are playing with these multi-pieceballs for several reasons including new manufacturing technologies,lower material costs, and desirable ball playing performance properties.Many golf balls used today have multi-layered cores comprising an innercore and at least one surrounding outer core layer. For example, theinner core may be made of a relatively soft and resilient material,while the outer core may be made of a harder and more rigid material.The “dual-core” sub-assembly is encapsulated by a single ormulti-layered cover to provide a final ball assembly. Differentmaterials are used in these golf ball constructions to impart specificproperties and playing features to the ball.

For instance, in recent years, there has been high interest in usingpolyurethane compositions to make golf ball covers. Basically,polyurethane compositions contain urethane linkages formed by reactingan isocyanate group (—N═C═O) with a hydroxyl group (OH). Polyurethanesare produced by the reaction of a multi-functional isocyanate with apolyol in the presence of a catalyst and other additives. The chainlength of the polyurethane prepolymer is extended by reacting it withhydroxyl-terminated and amine curing agents.

In Sullivan et al., U.S. Pat. No. 5,971,870, thermoplastic orthermosetting polyurethanes and ionomers are described as being suitablematerials for making outer cover and any inner cover layer. The coverlayers can be formed over the cores by injection-molding, compressionmolding, casting or other conventional molding techniques. Preferably,each cover layer is separately formed. In one embodiment, the innercover layer is first injection molded over the core in a cavity mold,subsequently any intermediate cover layers are injection molded over theinner cover layer in a cavity mold, and finally the outer cover layer isinjection molded over the intermediate cover layers in a dimpled cavitymold.

In Sullivan et al., U.S. Pat. No. 7,131,915, the outer cover can be madefrom a polyurethane composition and various aliphatic and aromaticdiisocyanates are described as being suitable for making thepolyurethanes. Depending on the type of curing agent used, thepolyurethane composition may be thermoplastic or thermoset in nature.Sullivan '915 further discloses that compositions for the intermediatecover layer and inner cover layer may be selected from the same class ofmaterials as used for the outer cover layer. In other embodiments,ionomers such as HNPs, can be used to form the intermediate and innercover layers. The castable, reactive liquid used to form the urethaneelastomer material can be applied over the core using a variety oftechniques such as spraying, dipping, spin coating, or flow coatingmethods.

As discussed above, both thermoplastic and thermosetting polyurethanescan be used to form golf ball covers. Thermoplastic polyurethanes haveminimal cross-linking; any bonding in the polymer network is primarilythrough hydrogen bonding or other physical mechanism. Because of theirlower level of cross-linking, thermoplastic polyurethanes are relativelyflexible. The cross-linking bonds in thermoplastic polyurethanes can bereversibly broken by increasing temperature such as during molding orextrusion. That is, the theremoplastic material softens when exposed toheat and returns to its original condition when cooled. On the otherhand, thermoset polyurethanes become irreversibly set when they arecured. The cross-linking bonds are irreversibly set and are not brokenwhen exposed to heat. Thus, thermoset polyurethanes, which typicallyhave a high level of cross-linking, are relatively rigid.

One advantage with using thermoplastic polyurethane compositions to formgolf ball covers is that they have good processability. Thethermoplastic polyurethanes generally have good melt-flow properties anddifferent molding methods may be used to form the covers. Althoughthermoplastic polyurethane covers for golf balls have been used over theyears, there are drawbacks with using some thermoplastic polyurethanesmaterials. For example, one drawback with some thermoplasticpolyurethanes is they may not be as durable and tough as other polymers.For example, the resulting thermoplastic polyurethane cover may not havehigh mechanical strength, impact durability, and cut and scuff (grooveshear)-resistance.

Thus, manufacturers have used various methods of treating thermoplasticpolyurethanes to enhance the durability and strength of the polymer. Forexample, an isocyanate may be compounded into a masterbatch and then themasterbatch may be added to the thermoplastic polyurethane compositionprior to molding. In another example, the molded thermoplasticpolyurethane cover may be dipped into an isocyanate solution. Treatingthe thermoplastic polyurethane material with isocyanates helps improvethe physical properties such as mechanical strength, impact durability,and cut and scuff (groove shear)-resistance of the material. In somecases, the physical properties may not only increase, but they mayactually increase beyond the values of the non-refined material.

For example, Kennedy, III, U.S. Pat. No. 8,920,264 and Matroni, U.S.Pat. No. 9,119,990 disclose isocyanate dipping methods, whereby a golfball having a thermoplastic polyurethane cover is treated with asolution of isocyanate. The isocyanate solution can contain a solvent,for example, acetone or methyl ethyl ketone (MEK), at least oneisocyanate compound, and a catalyst. The ball is soaked in theisocyanate solution and this causes the isocyanate compound to permeatethe cover. The isocyanate compound cross-links the thermoplasticpolyurethane cover material, and this improves the physical propertiesof the cover such as durability and scuff-resistance.

One drawback with using conventional isocyanate treatment methods isthey typically require additional steps in the manufacturing process andthey may not be very cost-effective. These additional steps may betime-consuming and reduce process efficiency. In view of some of thedrawbacks with some of these methods, it would be desirable to have new,cost-effective, efficient methods that can produce golf balls withdesirable physical and playing performance properties. The presentinvention provides new methods for making thermoplastic polyurethanecovers for golf balls having many advantageous features and benefits.The invention also includes the resulting golf balls having goodphysical and playing performance properties.

SUMMARY OF THE INVENTION

The present invention generally relates to golf balls having covers madeof thermoplastic polyurethane compositions. The invention includesmethods for applying polyurethane coatings to the thermoplasticpolyurethane cover. In one embodiment, a method for forming a coatedgolf ball comprises the steps of: a) providing a golf ball comprising atleast one core layer and an outer cover layer, wherein the outer coverlayer is formed from a thermoplastic polyurethane composition; b)applying a first polyurethane coating comprising unreacted isocyanategroups and having an isocyanate index of at least about 115 to the outercover layer; c) treating the golf ball with heat; and d) applying asecond polyurethane coating to the outer cover of the golf ball to forma coated golf ball. In a second embodiment, the second polyurethanecoating has an isocyanate index of less than 96. The first and secondpolyurethane coatings can be applied by spray-coating. Also, the outersurface of the golf ball can be heated with a source of infrared heat,preferably to a surface temperature in the range of about 120° to 150°F.

Preferably, at least one of the first and second polyurethane coatingscomprises a catalyst. The thermoplastic polyurethane composition alsomay comprise a catalyst. Suitable catalysts include, for example, thoseselected from the group consisting of dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diaza compounds, and potassiumacetate, and.

In one embodiment, the outer cover layer has a thickness in the range ofabout 0.010 to about 0.050 inches and hardness in the range of about 20to about 59 Shore D. The golf ball may include an inner core and outercore layer. The golf ball also may include an inner cover layer.

In another embodiment, the steps comprise: a) providing a golf ballhaving an outer cover layer formed from a thermoplastic polyurethanecomposition; b) applying a mixture comprising multi-functionalisocyanate and solvent to the outer cover layer; c) applying a firstpolyurethane coating comprising unreacted isocyanate groups and havingan isocyanate index of at least about 115 to the outer cover layer; c)treating the golf ball with heat; and d) applying a second polyurethanecoating to the outer cover of the golf ball to form a coated golf ball.In another embodiment, the first polyurethane coating is notover-indexed. For example, the first polyurethane coating can have anisocyanate index of less than 96. The mixture applied to the outer coverlayer can comprise a multi-functional isocyanate, ultraviolet (UV) lightstabilizer, and solvent.

In yet another embodiment, the first polyurethane coating comprises amixture of 1,6-hexamethylene diisocyanate (HDI);4,4′-dicyclohexylmethane diisocyanate (H₁₂ MDI); and 4,4′-methylenediphenyl diisocyanate (MDI); and solvent. Suitable solvents include, forexample, ketones, acetates, and mixtures thereof. The invention alsoincludes the balls made from the above-described methods. The finishedballs have many advantageous physical and playing performanceproperties.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a perspective view of a dimpled golf ball made in accordancewith the present invention;

FIG. 2 is a cross-sectional view of a two-piece golf ball having aninner core and outer cover made in accordance with the presentinvention;

FIG. 3 is a cross-sectional view of another two-piece golf ball havingan inner core and outer cover made in accordance with the presentinvention;

FIG. 4 is a cross-sectional view of a three-piece golf ball having aninner core, outer core, and outer cover made in accordance with thepresent invention;

FIG. 5 is a partial cut-away perspective view of a three-piece golf ballhaving an inner core, outer core, and outer cover made in accordancewith the present invention; and

FIG. 6 is a cross-sectional view of a four-piece golf ball having aninner core, outer core, inner cover, and outer cover made in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to golf balls having covers madeof thermoplastic polyurethane (TPU) compositions. Different polyurethaneprimer and top-coats are applied to the polyurethane outer cover inaccordance with this invention. The invention also includes the finishedgolf balls made from these coating applications.

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a two-piece golf ballcontaining a core and having a surrounding cover is made. Three-piecegolf balls containing a dual-layered core and single-layered cover alsocan be made. The dual-core includes an inner core (center) andsurrounding outer core layer. In another version, a four-piece golf ballcontaining a dual-core and dual-cover (inner cover and outer coverlayers) is made. In yet another construction, a four-piece or five-piecegolf ball containing a dual-core; casing layer(s); and cover layer(s)may be made. As used herein, the term, “casing layer” means a layer ofthe ball disposed between the multi-layered core sub-assembly and cover.The casing layer also may be referred to as a mantle or intermediatelayer. The diameter and thickness of the different layers along withproperties such as hardness and compression may vary depending upon theconstruction and desired playing performance properties of the golf ballas discussed further below.

Core Structure

The golf ball may contain a single- or multi-layered core. In onepreferred embodiment, at least one of the core layers is formed of arubber composition comprising polybutadiene rubber material. Moreparticularly, in one version, the ball contains a single inner coreformed of the polybutadiene rubber composition. In a second version, theball contains a dual-core comprising an inner core (center) andsurrounding outer core layer.

In one version, the core is formed of a rubber composition comprising arubber material such as, for example, polybutadiene, ethylene-propylenerubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadienerubber, polyalkenamers, butyl rubber, halobutyl rubber, or polystyreneelastomers. For example, polybutadiene rubber compositions may be usedto form the inner core (center) and surrounding outer core layer in adual-layer construction. In another version, the core may be formed froman ionomer composition comprising an ethylene acid copolymer containingacid groups such that greater than 70% of the acid groups areneutralized. These highly neutralized polymers (HNPs) also may be usedto form at least one core layer in a multi-layered core construction.For example, a polybutadiene rubber composition may be used to form thecenter and a HNP composition may be used to form the outer core. Suchrubber and HNP compositions are discussed in further detail below.

In general, polybutadiene is a homopolymer of 1, 3-butadiene. The doublebonds in the 1, 3-butadiene monomer are attacked by catalysts to growthe polymer chain and form a polybutadiene polymer having a desiredmolecular weight. Any suitable catalyst may be used to synthesize thepolybutadiene rubber depending upon the desired properties. Normally, atransition metal complex (for example, neodymium, nickel, or cobalt) oran alkyl metal such as alkyllithium is used as a catalyst. Othercatalysts include, but are not limited to, aluminum, boron, lithium,titanium, and combinations thereof. The catalysts produce polybutadienerubbers having different chemical structures. In a cis-bondconfiguration, the main internal polymer chain of the polybutadieneappears on the same side of the carbon-carbon double bond contained inthe polybutadiene. In a trans-bond configuration, the main internalpolymer chain is on opposite sides of the internal carbon-carbon doublebond in the polybutadiene. The polybutadiene rubber can have variouscombinations of cis- and trans-bond structures. A preferredpolybutadiene rubber has a 1,4 cis-bond content of at least 40%,preferably greater than 80%, and more preferably greater than 90%. Ingeneral, polybutadiene rubbers having a high 1,4 cis-bond content havehigh tensile strength. The polybutadiene rubber may have a relativelyhigh or low Mooney viscosity.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; and DIENE 55NF, 70AC, and 320 AC, availablefrom Firestone Polymers of Akron, Ohio.

To form the core, the polybutadiene rubber is used in an amount of atleast about 5% by weight based on total weight of composition and isgenerally present in an amount of about 5% to about 100%, or an amountwithin a range having a lower limit of 5% or 10% or 20% or 30% or 40% or50% and an upper limit of 55% or 60% or 70% or 80% or 90% or 95% or100%. In general, the concentration of polybutadiene rubber is about 45to about 95 weight percent. Preferably, the rubber material used to formthe core layer comprises at least 50% by weight, and more preferably atleast 70% by weight, polybutadiene rubber.

The rubber compositions of this invention may be cured, either bypre-blending or post-blending, using conventional curing processes.Suitable curing processes include, for example, peroxide-curing,sulfur-curing, high-energy radiation, and combinations thereof.Preferably, the rubber composition contains a free-radical initiatorselected from organic peroxides, high energy radiation sources capableof generating free-radicals, and combinations thereof. In one preferredversion, the rubber composition is peroxide-cured. Suitable organicperoxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions preferably include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur or metal saltthereof, organic disulfide, or inorganic disulfide compounds may beadded to the rubber composition. These compounds also may function as“soft and fast agents.” As used herein, “soft and fast agent” means anycompound or a blend thereof that is capable of making a core: 1) softer(having a lower compression) at a constant “coefficient of restitution”(COR); and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

The rubber compositions of the present invention also may include“fillers,” which are added to adjust the density and/or specific gravityof the material. Suitable fillers include, but are not limited to,polymeric or mineral fillers, metal fillers, metal alloy fillers, metaloxide fillers and carbonaceous fillers. The fillers can be in anysuitable form including, but not limited to, flakes, fibers, whiskers,fibrils, plates, particles, and powders. Rubber regrind, which isground, recycled rubber material (for example, ground to about 30 meshparticle size) obtained from discarded rubber golf ball cores, also canbe used as a filler. The amount and type of fillers utilized aregoverned by the amount and weight of other ingredients in the golf ball,since a maximum golf ball weight of 45.93 g (1.62 ounces) has beenestablished by the United States Golf Association (USGA).

Suitable polymeric or mineral fillers that may be added to the rubbercomposition include, for example, precipitated hydrated silica, clay,talc, asbestos, glass fibers, aramid fibers, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,tungsten carbide, diatomaceous earth, polyvinyl chloride, carbonatessuch as calcium carbonate and magnesium carbonate. Suitable metalfillers include titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, lead, copper, boron, cobalt, beryllium, zinc, and tin.Suitable metal alloys include steel, brass, bronze, boron carbidewhiskers, and tungsten carbide whiskers. Suitable metal oxide fillersinclude zinc oxide, iron oxide, aluminum oxide, titanium oxide,magnesium oxide, and zirconium oxide. Suitable particulate carbonaceousfillers include graphite, carbon black, cotton flock, natural bitumen,cellulose flock, and leather fiber. Micro balloon fillers such as glassand ceramic, and fly ash fillers can also be used. In a particularaspect of this embodiment, the rubber composition includes filler(s)selected from carbon black, nanoclays (e.g., Cloisite® and Nanofil®nanoclays, commercially available from Southern Clay Products, Inc., andNanomax® and Nanomer® nanoclays, commercially available from Nanocor,Inc.), talc (e.g., Luzenac HAR® high aspect ratio talcs, commerciallyavailable from Luzenac America, Inc.), glass (e.g., glass flake, milledglass, and microglass), mica and mica-based pigments (e.g., Iriodin®pearl luster pigments, commercially available from The Merck Group), andcombinations thereof. In a particular embodiment, the rubber compositionis modified with organic fiber micropulp.

In addition, the rubber compositions may include antioxidants to preventthe breakdown of the elastomers. Also, processing aids such as highmolecular weight organic acids and salts thereof, may be added to thecomposition. In a particular embodiment, the total amount of additive(s)and filler(s) present in the rubber composition is 15 wt % or less, or12 wt % or less, or 10 wt % or less, or 9 wt % or less, or 6 wt % orless, or 5 wt % or less, or 4 wt % or less, or 3 wt % or less, based onthe total weight of the rubber composition.

The polybutadiene rubber material (base rubber) may be blended withother elastomers in accordance with this invention. Other elastomersinclude, but are not limited to, polybutadiene, polyisoprene, ethylenepropylene rubber (“EPR”), styrene-butadiene rubber, styrenic blockcopolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and thelike, where “S” is styrene, “I” is isobutylene, and “B” is butadiene),polyalkenamers such as, for example, polyoctenamer, butyl rubber,halobutyl rubber, polystyrene elastomers, polyethylene elastomers,polyurethane elastomers, polyurea elastomers, metallocene-catalyzedelastomers and plastomers, copolymers of isobutylene and p-alkylstyrene,halogenated copolymers of isobutylene and p-alkylstyrene, copolymers ofbutadiene with acrylonitrile, polychloroprene, alkyl acrylate rubber,chlorinated isoprene rubber, acrylonitrile chlorinated isoprene rubber,and combinations of two or more thereof.

The polymers, free-radical initiators, filler, cross-linking agents, andany other materials used in forming either the golf ball center or anyportion of the core, in accordance with invention, may be combined toform a mixture by any type of mixing known to one of ordinary skill inthe art. Suitable types of mixing include single pass and multi-passmixing, and the like. The cross-linking agent, and any other optionaladditives used to modify the characteristics of the golf ball center oradditional layer(s), may similarly be combined by any type of mixing. Asingle-pass mixing process where ingredients are added sequentially ispreferred, as this type of mixing tends to increase efficiency andreduce costs for the process. The preferred mixing cycle is single stepwherein the polymer, cis-to-trans catalyst, filler, zinc diacrylate, andperoxide are added in sequence.

In one preferred embodiment, the entire core or at least one core layerin a multi-layered structure is formed of a rubber compositioncomprising a material selected from the group of natural and syntheticrubbers including, but not limited to, polybutadiene, polyisoprene,ethylene propylene rubber (“EPR”), ethylene-propylene-diene (“EPDM”)rubber, styrene-butadiene rubber, styrenic block copolymer rubbers (suchas “SI”, “SIS”, “SB”, “SBS”, “SIBS”, and the like, where “S” is styrene,“I” is isobutylene, and “B” is butadiene), polyalkenamers such as, forexample, polyoctenamer, butyl rubber, halobutyl rubber, polystyreneelastomers, polyethylene elastomers, polyurethane elastomers, polyureaelastomers, metallocene-catalyzed elastomers and plastomers, copolymersof isobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and combinations of two ormore thereof.

As discussed above, single and multi-layered cores can be made inaccordance with this invention. In two-layered cores, a thermosetmaterial such as, for example, thermoset rubber, can be used to make theouter core layer or a thermoplastic material such as, for example,ethylene acid copolymer containing acid groups that are at leastpartially or fully neutralized can be used to make the outer core layer.Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. Suitable ethylene acid copolymer ionomers and otherthermoplastics that can be used to form the core layer(s) are the samematerials that can be used to make an inner cover layer as discussedfurther below.

In another example, multi-layered cores having an inner core,intermediate core layer, and outer core layer, wherein the intermediatecore layer is disposed between the intermediate and outer core layersmay be prepared in accordance with this invention. More particularly, asdiscussed above, the inner core may be constructed from a thermoplasticor thermoset composition, such as thermoset rubber. Meanwhile, theintermediate and outer core layers also may be formed from thermoset orthermoplastic materials. Suitable thermoset and thermoplasticcompositions that may be used to form the intermediate/outer core layersare discussed above. For example, each of the intermediate and outercore layers may be formed from a thermoset rubber composition. Thus, theintermediate core layer may be formed from a first thermoset rubbercomposition; and the outer core layer may be formed from a secondthermoset rubber composition. In another embodiment, the intermediatecore layer is formed from a thermoset composition; and the outer corelayer is formed from a thermoplastic composition. In a third embodiment,the intermediate core layer is formed from a thermoplastic composition;and the outer core layer is formed from a thermoset composition.Finally, in a fourth embodiment, the intermediate core layer is formedfrom a first thermoplastic composition; and the outer core layer isformed from a second thermoplastic compositions.

In a particular embodiment, the core includes at least one additionalthermoplastic intermediate core layer formed from a compositioncomprising an ionomer selected from DuPont® HPF ESX 367, HPF 1000, HPF2000, HPF AD1035, HPF AD1035 Soft, HPF AD1040, and AD1172 ionomers,commercially available from E. I. du Pont de Nemours and Company. Thecoefficient of restitution (“COR”), compression, and surface hardness ofeach of these materials, as measured on 1.55″ injection molded spheresaged two weeks at 23° C./50% RH, are given in Table 1 below.

TABLE 1 Solid Solid Sphere Solid Sphere Shore D Example Sphere CORCompression Surface Hardness HPF 1000 0.830 115 54 HPF 2000 0.860 90 47HPF AD1035 0.820 63 42 HPF AD1035 Soft 0.780 33 35 HPF AD 1040 0.855 13560 HPF AD1172 0.800 32 37

Cover Layer Structure

The golf balls of this invention further include an outer cover layermade of a thermoplastic polyurethane composition. In general,polyurethanes contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of a multi-functional isocyanate (NCO—R—NCO)with a long-chain polyol having terminal hydroxyl groups (OH—OH) in thepresence of a catalyst and other additives. The chain length of thepolyurethane prepolymer is extended by reacting it with short-chaindiols (OH—R′—OH). The resulting polyurethane has elastomeric propertiesbecause of its “hard” and “soft” segments, which are covalently bondedtogether. This phase separation occurs because the mainly non-polar, lowmelting soft segments are incompatible with the polar, high melting hardsegments. The hard segments, which are formed by the reaction of thediisocyanate and low molecular weight chain-extending diol, arerelatively stiff and immobile. The soft segments, which are formed bythe reaction of the diisocyanate and long chain diol, are relativelyflexible and mobile. Because the hard segments are covalently coupled tothe soft segments, they inhibit plastic flow of the polymer chains, thuscreating elastomeric resiliency.

By the term, “isocyanate compound” as used herein, it is meant anyaliphatic or aromatic isocyanate containing two or more isocyanatefunctional groups. The isocyanate compounds can be monomers or monomericunits, because they can be polymerized to produce polymeric isocyanatescontaining two or more monomeric isocyanate repeat units. The isocyanatecompound may have any suitable backbone chain structure includingsaturated or unsaturated, and linear, branched, or cyclic. By the term,“polyamine” as used herein, it is meant any aliphatic or aromaticcompound containing two or more primary or secondary amine functionalgroups. The polyamine compound may have any suitable backbone chainstructure including saturated or unsaturated, and linear, branched, orcyclic. The term “polyamine” may be used interchangeably withamine-terminated component. By the term, “polyol” as used herein, it ismeant any aliphatic or aromatic compound containing two or more hydroxylfunctional groups. The term “polyol” may be used interchangeably withhydroxy-terminated component.

Thermoplastic polyurethanes have minimal cross-linking; any bonding inthe polymer network is primarily through hydrogen bonding or otherphysical mechanism. Because of their lower level of cross-linking,thermoplastic polyurethanes are relatively flexible. The cross-linkingbonds in thermoplastic polyurethanes can be reversibly broken byincreasing temperature such as during molding or extrusion. That is, thetheremoplastic material softens when exposed to heat and returns to itsoriginal condition when cooled. On the other hand, thermosetpolyurethanes become irreversibly set when they are cured. Thecross-linking bonds are irreversibly set and are not broken when exposedto heat. Thus, thermoset polyurethanes, which typically have a highlevel of cross-linking, are relatively rigid.

Aromatic polyurethanes can be prepared in accordance with this inventionand these materials are preferably formed by reacting an aromaticdiisocyanate with a polyol. Suitable aromatic diisocyanates that may beused in accordance with this invention include, for example, toluene2,4-diisocyanate (TDI), toluene 2,6-diisocyanate (TDI), 4,4′-methylenediphenyl diisocyanate (MDI), 2,4′-methylene diphenyl diisocyanate (MDI),polymeric methylene diphenyl diisocyanate (PMDI), p-phenylenediisocyanate (PPDI), m-phenylene diisocyanate (PDI), naphthalene1,5-diisocynate (NDI), naphthalene 2,4-diisocyanate (NDI), p-xylenediisocyanate (XDI), and homopolymers and copolymers and blends thereof.The aromatic isocyanates are able to react with the hydroxyl or aminecompounds and form a durable and tough polymer having a high meltingpoint. The resulting polyurethane generally has good mechanical strengthand cut/shear-resistance.

Aliphatic polyurethanes also can be prepared in accordance with thisinvention and these materials are preferably formed by reacting analiphatic diisocyanate with a polyol. Suitable aliphatic diisocyanatesthat may be used in accordance with this invention include, for example,isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI),4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI”),meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexanediisocyanate (CHDI), and homopolymers and copolymers and blends thereof.Particularly suitable multi-functional isocyanates include trimers ofHDI or H₁₂ MDI, oligomers, or other derivatives thereof. The resultingpolyurethane generally has good light and thermal stability.

Any polyol available to one of ordinary skill in the art is suitable foruse according to the invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG) which isparticularly preferred, polyethylene propylene glycol, polyoxypropyleneglycol, and mixtures thereof. The hydrocarbon chain can have saturatedor unsaturated bonds and substituted or unsubstituted aromatic andcyclic groups.

In another embodiment, polyester polyols are included in thepolyurethane material. Suitable polyester polyols include, but are notlimited to, polyethylene adipate glycol; polybutylene adipate glycol;polyethylene propylene adipate glycol; o-phthalate-1,6-hexanediol;poly(hexamethylene adipate) glycol; and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups. In stillanother embodiment, polycaprolactone polyols are included in thematerials of the invention. Suitable polycaprolactone polyols include,but are not limited to: 1,6-hexanediol-initiated polycaprolactone,diethylene glycol initiated polycaprolactone, trimethylol propaneinitiated polycaprolactone, neopentyl glycol initiated polycaprolactone,1,4-butanediol-initiated polycaprolactone, and mixtures thereof. Thehydrocarbon chain can have saturated or unsaturated bonds, orsubstituted or unsubstituted aromatic and cyclic groups. In yet anotherembodiment, polycarbonate polyols are included in the polyurethanematerial of the invention. Suitable polycarbonates include, but are notlimited to, polyphthalate carbonate and poly(hexamethylene carbonate)glycol. The hydrocarbon chain can have saturated or unsaturated bonds,or substituted or unsubstituted aromatic and cyclic groups. In oneembodiment, the molecular weight of the polyol is from about 200 toabout 4000.

There are two basic techniques that can be used to make thepolyurethanes: a) one-shot technique, and b) prepolymer technique. Inthe one-shot technique, the diisocyanate, polyol, andhydroxyl-terminated chain-extender (curing agent) are reacted in onestep. On the other hand, the prepolymer technique involves a firstreaction between the diisocyanate and polyol compounds to produce apolyurethane prepolymer, and a subsequent reaction between theprepolymer and hydroxyl-terminated chain-extender. As a result of thereaction between the isocyanate and polyol compounds, there will be someunreacted NCO groups in the polyurethane prepolymer. The prepolymershould have less than 14% unreacted NCO groups. Preferably, theprepolymer has no greater than 8.5% unreacted NCO groups, morepreferably from 2.5% to 8%, and most preferably from 5.0% to 8.0%unreacted NCO groups. As the weight percent of unreacted isocyanategroups increases, the hardness of the composition also generallyincreases.

Either the one-shot or prepolymer method may be employed to produce thepolyurethane compositions of the invention. In one embodiment, theone-shot method is used, wherein the isocyanate compound is added to areaction vessel and then a curative mixture comprising the polyol andcuring agent is added to the reaction vessel. The components are mixedtogether so that the molar ratio of isocyanate groups to hydroxyl groupsis preferably in the range of about 1.00:1.00 to about 1.10:1.00. In asecond embodiment, the prepolymer method is used. In general, theprepolymer technique is preferred because it provides better control ofthe chemical reaction. The prepolymer method provides a more homogeneousmixture resulting in a more consistent polymer composition. The one-shotmethod results in a mixture that is inhomogeneous (more random) andaffords the manufacturer less control over the molecular structure ofthe resultant composition.

The polyurethane compositions can be formed by chain-extending thepolyurethane prepolymer with a single chain-extender or blend ofchain-extenders as described further below. As discussed above, thepolyurethane prepolymer can be chain-extended by reacting it with asingle chain-extender or blend of chain-extenders. In general, theprepolymer can be reacted with hydroxyl-terminated curing agents,amine-terminated curing agents, and mixtures thereof. The curing agentsextend the chain length of the prepolymer and build-up its molecularweight. In general, thermoplastic polyurethane compositions aretypically formed by reacting the isocyanate blend and polyols at a 1:1stoichiometric ratio. Thermoset compositions, on the other hand, arecross-linked polymers and are typically produced from the reaction ofthe isocyanate blend and polyols at normally a 1.05:1 stoichiometricratio

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds for producing the prepolymer or betweenprepolymer and chain-extender during the chain-extending step.Preferably, the catalyst is added to the reactants before producing theprepolymer. Suitable catalysts include, but are not limited to, bismuthcatalyst; zinc octoate; stannous octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, and tributylamine; organic acids such as oleic acid andacetic acid; delayed catalysts; and mixtures thereof. The catalyst ispreferably added in an amount sufficient to catalyze the reaction of thecomponents in the reactive mixture. In one embodiment, the catalyst ispresent in an amount from about 0.001 percent to about 1 percent, andpreferably 0.1 to 0.5 percent, by weight of the composition.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3T-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”); andmixtures thereof. One particularly suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When the polyurethane prepolymer is reacted with hydroxyl-terminatedcuring agents during the chain-extending step, as described above, theresulting polyurethane composition contains urethane linkages. On theother hand, when the polyurethane prepolymer is reacted withamine-terminated curing agents during the chain-extending step, anyexcess isocyanate groups in the prepolymer will react with the aminegroups in the curing agent. The resulting polyurethane compositioncontains urethane and urea linkages and may be referred to as apolyurethane/urea hybrid. The concentration of urethane and urealinkages in the hybrid composition may vary. In general, the hybridcomposition may contain a mixture of about 10 to 90% urethane and about90 to 10% urea linkages.

More particularly, when the polyurethane prepolymer is reacted withhydroxyl-terminated curing agents during the chain-extending step, asdescribed above, the resulting composition is essentially a purepolyurethane composition containing urethane linkages having thefollowing general structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons.

However, when the polyurethane prepolymer is reacted with anamine-terminated curing agent during the chain-extending step, anyexcess isocyanate groups in the prepolymer will react with the aminegroups in the curing agent and create urea linkages having the followinggeneral structure:

where x is the chain length, i.e., about 1 or greater, and R and R₁ arestraight chain or branched hydrocarbon chain having about 1 to about 20carbons.

The polyurethane compositions used to form the cover layer may containother polymer materials including, for example: aliphatic or aromaticpolyurethanes, aliphatic or aromatic polyureas, aliphatic or aromaticpolyurethane/urea hybrids, olefin-based copolymer ionomer compositions,polyethylene, including, for example, low density polyethylene, linearlow density polyethylene, and high density polyethylene; polypropylene;rubber-toughened olefin polymers; acid copolymers, for example,poly(meth)acrylic acid, which do not become part of an ionomericcopolymer; plastomers; flexomers; styrene/butadiene/styrene blockcopolymers; styrene/ethylene-butylene/styrene block copolymers;dynamically vulcanized elastomers; copolymers of ethylene and vinylacetates; copolymers of ethylene and methyl acrylates; polyvinylchloride resins; polyamides, poly(amide-ester) elastomers, and graftcopolymers of ionomer and polyamide including, for example, Pebax®thermoplastic polyether block amides, available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, available from DuPont;polyurethane-based thermoplastic elastomers, such as Elastollan®,available from BASF; polycarbonate/polyester blends such as Xylex®,available from SABIC Innovative Plastics; maleic anhydride-graftedpolymers such as Fusabond®, available from DuPont; and mixtures of theforegoing materials.

In addition, the polyurethane compositions may contain fillers,additives, and other ingredients that do not detract from the propertiesof the final composition. These additional materials include, but arenot limited to, catalysts, wetting agents, coloring agents, opticalbrighteners, cross-linking agents, whitening agents such as titaniumdioxide and zinc oxide, ultraviolet (UV) light absorbers, hindered aminelight stabilizers, defoaming agents, processing aids, surfactants, andother conventional additives. Other suitable additives includeantioxidants, stabilizers, softening agents, plasticizers, includinginternal and external plasticizers, impact modifiers, foaming agents,density-adjusting fillers, reinforcing materials, compatibilizers, andthe like. Some examples of useful fillers include zinc oxide, zincsulfate, barium carbonate, barium sulfate, calcium oxide, calciumcarbonate, clay, tungsten, tungsten carbide, silica, and mixturesthereof. Rubber regrind (recycled core material) and polymeric, ceramic,metal, and glass microspheres also may be used. Generally, the additiveswill be present in the composition in an amount between about 1 andabout 70 weight percent based on total weight of the compositiondepending upon the desired properties.

Intermediate Layers

In one preferred embodiment, an intermediate layer is disposed betweenthe single or multi-layered core and surrounding cover layer. Theseintermediate layers also can be referred to as casing or inner coverlayers. The intermediate layer can be formed from any materials known inthe art, including thermoplastic and thermosetting materials, butpreferably is formed of an ionomer composition comprising an ethyleneacid copolymer containing acid groups that are at least partiallyneutralized. Suitable ethylene acid copolymers that may be used to formthe intermediate layers are generally referred to as copolymers ofethylene; C₃ to C₈ α, β-ethylenically unsaturated mono- or dicarboxylicacid; and optional softening monomer. These ethylene acid copolymerionomers also can be used to form the inner core and outer core layersas described above.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized. Preferred ionomers are salts of O/X- andO/X/Y-type acid copolymers, wherein O is an α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer. O is preferably selected from ethylene and propylene. X ispreferably selected from methacrylic acid, acrylic acid, ethacrylicacid, crotonic acid, and itaconic acid. Methacrylic acid and acrylicacid are particularly preferred. Y is preferably selected from (meth)acrylate and alkyl (meth) acrylates wherein the alkyl groups have from 1to 8 carbon atoms, including, but not limited to, n-butyl (meth)acrylate, isobutyl (meth) acrylate, methyl (meth) acrylate, and ethyl(meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred a, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is aC₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α, β-ethylenically unsaturated mono-or dicarboxylic acid in the acid copolymer is typically from 1 wt. % to35 wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5wt. % to 25 wt. %, and even more preferably from 10 wt. % to 20 wt. %,based on total weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed in U.S.Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference. The acid copolymer can be reacted withthe optional high molecular weight organic acid and the cation sourcesimultaneously, or prior to the addition of the cation source. Suitablecation sources include, but are not limited to, metal ion sources, suchas compounds of alkali metals, alkaline earth metals, transition metals,and rare earth elements; ammonium salts and monoamine salts; andcombinations thereof. Preferred cation sources are compounds ofmagnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals.

Other suitable thermoplastic polymers that may be used to form theintermediate layer include, but are not limited to, the followingpolymers (including homopolymers, copolymers, and derivatives thereof:(a) polyester, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof; (b) polyamides, polyamide-ethers, andpolyamide-esters, and those disclosed in U.S. Pat. Nos. 6,187,864,6,001,930, and 5,981,654, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof; (c)polyurethanes, polyureas, polyurethane-polyurea hybrids, and blends oftwo or more thereof; (d) fluoropolymers, such as those disclosed in U.S.Pat. Nos. 5,691,066, 6,747,110 and 7,009,002, the entire disclosures ofwhich are hereby incorporated herein by reference, and blends of two ormore thereof; (e) polystyrenes, such as poly(styrene-co-maleicanhydride), acrylonitrile-butadiene-styrene, poly(styrene sulfonate),polyethylene styrene, and blends of two or more thereof; (f) polyvinylchlorides and grafted polyvinyl chlorides, and blends of two or morethereof; (g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof; (h) polyethers, such as polyaryleneethers, polyphenylene oxides, block copolymers of alkenyl aromatics withvinyl aromatics and polyamicesters, and blends of two or more thereof;(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and (j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the core and intermediate layers in accordance withthis invention. For example, thermoplastic polyolefins such as linearlow density polyethylene (LLDPE), low density polyethylene (LDPE), andhigh density polyethylene (HDPE) may be cross-linked to form bondsbetween the polymer chains. The cross-linked thermoplastic materialtypically has improved physical properties and strength overnon-cross-linked thermoplastics, particularly at temperatures above thecrystalline melting point. Preferably a partially or fully-neutralizedionomer, as described above, is covalently cross-linked to render itinto a thermoset composition (that is, it contains at least some levelof covalent, irreversable cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Modifications in thermoplastic polymeric structure of thermoplastic canbe induced by a number of methods, including exposing the thermoplasticmaterial to high-energy radiation or through a chemical process usingperoxide. Radiation sources include, but are not limited to, gamma-rays,electrons, neutrons, protons, x-rays, helium nuclei, or the like. Gammaradiation, typically using radioactive cobalt atoms and allows forconsiderable depth of treatment, if necessary. For core layers requiringlower depth of penetration, electron-beam accelerators or UV and IRlight sources can be used. Useful UV and IR irradiation methods aredisclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, which areincorporated herein by reference. The thermoplastic core layers may beirradiated at dosages greater than 0.05 Mrd, preferably ranging from 1Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and most preferablyfrom 4 Mrd to 10 Mrd. In one preferred embodiment, the cores areirradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

Golf Ball Construction

The solid cores for the golf balls of this invention may be made usingany suitable conventional technique such as, for example, compression orinjection-molding. Typically, the cores are formed by compressionmolding a slug of uncured or lightly cured rubber material into aspherical structure. Prior to forming the cover layer, the corestructure may be surface-treated to increase the adhesion between itsouter surface and adjacent layer. Such surface-treatment may includemechanically or chemically-abrading the outer surface of the core. Forexample, the core may be subjected to corona-discharge,plasma-treatment, silane-dipping, or other treatment methods known tothose in the art. The cover layers are formed over the core or ballsub-assembly (the core structure and any intermediate layers disposedabout the core) using any suitable method as described further below.Prior to forming the cover layers, the ball sub-assembly may besurface-treated to increase the adhesion between its outer surface andthe overlying cover material using the above-described techniques.

Conventional compression and injection-molding and other methods can beused to form cover layers over the core or ball sub-assembly. Ingeneral, compression molding normally involves first making half(hemispherical) shells by injection-molding the composition in aninjection mold. This produces semi-cured, semi-rigid half-shells (orcups). Then, the half-shells are positioned in a compression mold aroundthe core or ball sub-assembly. Heat and pressure are applied and thehalf-shells fuse together to form a cover layer over the core orsub-assembly. Compression molding also can be used to cure the covercomposition after injection-molding. For example, a thermally-curablecomposition can be injection-molded around a core in an unheated mold.After the composition is partially hardened, the ball is removed andplaced in a compression mold. Heat and pressure are applied to the balland this causes thermal-curing of the outer cover layer.

Retractable pin injection-molding (RPIM) methods generally involve usingupper and lower mold cavities that are mated together. The upper andlower mold cavities form a spherical interior cavity when they arejoined together. The mold cavities used to form the outer cover layerhave interior dimple cavity details. The cover material conforms to theinterior geometry of the mold cavities to form a dimple pattern on thesurface of the ball. The injection-mold includes retractable supportpins positioned throughout the mold cavities. The retractable supportpins move in and out of the cavity. The support pins help maintain theposition of the core or ball sub-assembly while the molten compositionflows through the mold gates. The molten composition flows into thecavity between the core and mold cavities to surround the core and formthe cover layer. Other methods can be used to make the cover including,for example, reaction injection-molding (RIM), liquid injection-molding,casting, spraying, powder-coating, vacuum-forming, flow-coating,dipping, spin-coating, and the like.

As discussed above, an inner cover layer or intermediate layer,preferably formed from an ethylene acid copolymer ionomer composition,can be formed between the core or ball sub-assembly and cover layer. Theintermediate layer comprising the ionomer composition may be formedusing a conventional technique such as, for example, compression orinjection-molding. For example, the ionomer composition may beinjection-molded or placed in a compression mold to produce half-shells.These shells are placed around the core in a compression mold, and theshells fuse together to form an intermediate layer. Alternatively, theionomer composition is injection-molded directly onto the core usingretractable pin injection-molding.

Application of Primer and Top-Coats

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, and application of coatings in accordance with this invention.

For example, in traditional white-colored golf balls, thewhite-pigmented outer cover layer may be surface-treated using asuitable method such as, for example, corona, plasma, or ultraviolet(UV) light-treatment. In another finishing process, the golf balls arepainted with one or more paint coatings. For example, white or clearprimer paint may be applied first to the surface of the ball and thenindicia may be applied over the primer followed by application of aclear polyurethane top-coat. Indicia such as trademarks, symbols, logos,letters, and the like may be printed on the outer cover or prime-coatedlayer, or top-coated layer using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Any of the surfacecoatings may contain a fluorescent optical brightener.

In one embodiment, a first (primer) polyurethane coating comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 is applied to the outer cover. The golf ball is thenpreferably treated with heat so the coating is at least partially-cured.For example, the golf ball can be heated preferably to a surfacetemperature of at least about 105° to about 200° F. Preferably, the golfball is heated to a surface temperature of about 120° to about 150° F.Preferably, the golf ball is then heated for at a period of 2 minutes toabout 240 minutes, more preferably a period of 4 minutes to 120 minutes,and most preferably about 8 minutes to 60 minutes. In a third step, asecond (top-coat) polyurethane coating is applied to the outer cover.Any suitable coating technique may be used to apply the first and secondpolyurethane coatings. For example, spraying, dipping, brushing, orrolling methods can be used. Then the golf ball can go through a seriesof finishing steps.

In a second embodiment, a first (primer) polyurethane comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 is applied to the outer cover and the golf ball is treatedwith heat as described above. In a third step, a second (top-coat)polyurethane coating having an isocyanate index of less than 96 isapplied to the outer cover.

In a third embodiment, a first (primer) polyurethane comprisingunreacted isocyanate groups and having an isocyanate index of at leastabout 115 and further comprising a catalyst is applied to the outercover and the golf ball is treated with heat as described above. In athird step, a second (top-coat) polyurethane coating is applied to theouter cover as described above. The thermoplastic polyurethanecomposition of the outer cover layer and second (top-coat) polyurethanecoatings also may comprise catalysts. Suitable catalysts include, forexample, dibutyl tin dilaurate, dibutyl tin acetylacetonate, dibutyl tindibutoxide, dibutyl tin sulphide, dibutyl tin di-2-ethylhexanoate,dibutyl tin (IV) diacetate, dialkyltin (IV) oxide, tributyl tinlaurylmercaptate, dibutyl tin dichloride, organo lead, tetrabutyltitanate, tertiary amines, mercaptides, stannous octoate, potassiumoctoate, zinc octoate, diaza compounds, and potassium acetate, andmixtures thereof.

In a fourth embodiment, a mixture comprising a multi-functionalisocyanate and solvent is applied to the outer cover and the golf ballis treated with heat as described above. The mixture also may containadditives such as, for example, ultraviolet (UV) light stabilizers. Afirst (primer) polyurethane coating that may be over-indexed orunder-indexed may be applied to the outer cover. For example, themixture may be over-indexed and comprise unreacted isocyanate groups andhave an isocyanate index of at least about 115. In another example, themixture may be under indexed and have an isocyanate index of less than96. The golf ball is treated with heat as described above. A secondpolyurethane top-coating having an isocyanate index that is over-indexedor under-indexed may be applied. This treatment of the outer cover layerwith isocyanates further enhances cross-linking and improves coverdurability. These isocyanates can function as cross-linkers in thethermoplastic polyurethane cover. The chain length of the thermoplasticpolyurethane is extended and thus the molecular weight of thepolyurethane is increased when treated with the multi-functionalisocyanates.

Preferably, the multi-functional isocyanate compound is selected fromthe group consisting of toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocynate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and isophoronediisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI),4,4′-dicyclohexylmethane diisocyanate (“H₁₂ MDI”),meta-tetramethylxylyene diisocyanate (TMXDI), trans-cyclohexanediisocyanate (CHDI), and homopolymers and copolymers and blends thereof.More preferably, the polyisocyanate is selected from the groupconsisting of 4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylenediphenyl diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-dicyclohexylmethane diisocyanate (“H₁₂MDI”), p-phenylene diisocyanate (PPDI), and isophorone diisocyanate(IPDI), and homopolymers and copolymers and blends thereof.

The solvent may be any solvent that forms a solution with themulti-functional isocyanate and allows for some level of penetration ofthe isocyanate into the thermoplastic polyurethane substrate to which itis applied. Suitable solvents include, for example, toluene, xylene,naphthalene, ketones, and acetates. Preferably, the solvent comprisesone selected from the group consisting of acetone, methyl ethyl ketone,methyl amyl ketone, dimethyl heptanone, methyl pentanone, methylisobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, and butylacetate, and mixtures thereof. The mixture preferably comprises fromabout 1 to 25 wt. % isocyanate, and more preferably about 2 to 20 wt. %,and most preferably 5 to 18 wt % isocyanate.

Polyurethane Coatings and Isocyanate Index

Generally, the polyurethane coating material may be a two-part coatingsystem. A preferred coating system includes (1) a first part comprisinga polyol or another compound containing an active hydrogen atom, and (2)a second part comprising a polyisocyanate (or polyisocyanurate) with atleast two —N═C═O groups.

Suitable polyols for the polyurethane coating system include bothpolyether and polyester polyols. In one particular embodiment, thepolyol may be a hydroxyl functional polyol having a hydroxyl equivalentweight in the range of from about 50 to about 1500, or an hydroxylequivalent weight being in the range of from about 200 to about 800.Suitable polyesters for use herein include poly (oxydiethylene adipates)that are condensation products of diethylene glycol and adipic acid,branched with trimethylolpropane or pentaerythritol, andpolycaprolactone (hydroxycaproic acid) polyesters.

Suitable polyethers include polymers of propylene oxide or propyleneoxide/ethylene oxide. Such materials are usually triols or diols withmolecular weights between 1000 and 7000. Suitable examples of polyolsinclude Desmophen® 651A-65, 800, 670A-80, 680-70 and 631A-75, which aresaturated polyester resins, commercially available from Bayer Corp.

As mentioned above, in addition to a polyol, the two-part polyurethanesystem also comprises a polyisocyanate (or polyisocyanurate) with atleast two —N═C═O groups, carried in a solvent. Various diisocyantes,including but not limited to hexamethylene diisocyanate (HDI), methylenediisocyanate (MDI), toluene diisocyanate (TDI), and isophoronediisocyanate (IPDI) may be used. In particular embodiments, aliphaticisocyanates may be used. HDI derivatives contemplated for use herein aresold by Bayer Corp. under the trademark, Desmodur™. One such compositionis Desmodur™ N-3200, which is a low viscosity biuret of HDI.

The polyisocyanate used herein may have an equivalent weight within therange of from about 100 to about 1,200, or from about 150 to about 300in some embodiments. The polyisocyanate may be carried in a solvent,with the solvent solution containing from a minimum of about 40%,alternatively about 60%, alternatively about 70%, to a maximum ofapproaching 100%, and in particular about 85%, by weight of thepolyisocyanate.

Suitable solvents for the polyisocyanate include methyl isobutyl ketone,methyl amyl ketone, methyl isoamyl ketone, butyl acetate and propyleneglycol monomethyl ether acetate, or mixtures thereof. In a particularlyembodiment, the solvent is present in an amount of 20-65 weight %, or inamount of 40-60 weight % based upon the total weight of the coatingsystem. Urethane grade solvents (i.e. low-moisture solvents) may be usedin particular embodiments.

The polyurethane coating material may also be formed from a polyurethanesystem that includes a catalyst. Generally, the catalyst increases therate of curing. The catalyst may comprise at least one member selectedfrom the group consisting of dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diaza compounds, and potassiumacetate.

The catalyst may be present in a quantity of 0.01-10 weight activecatalyst (not including any carrier) based on total resin solids (polyolplus polyisocyanate, excluding solvents). The quantity of catalyst willdepend upon the type of catalyst, polyol, polyisocyanate, and solventswhich are used, as well as the curing temperature and desired curingtime. For example, when dibutyl tin dilaurate is used as the catalyst,it preferably is present in an amount of about 0.05-0.35 weight % activecatalyst based upon total resin solids, and more preferably 0.08-0.15weight % based upon total resin solids. Generally, the catalystpreferably is present in an amount sufficient to reduce the curing timeof the coating as compared to a coating system which does not containthe catalyst but is otherwise identical.

Any aromatic or aliphatic or blend thereof may be used includingpolyisocyanates. Preferred examples of the isocyanate component in thepolyurethane include: aromatic polyisocyanates such as 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, mixtures of 2,4-toluenediisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethanediisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI),tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate(PPDI); alicyclic polyisocyanates such as 4,4′-dicyclohexylmethanediisocyanate (H₁₂MDI), hydrogenated xylylene diisocyanate (H₆XDI) andisophorone diisocyanate (IPDI); and aliphatic polyisocyanates such ashexamethylene diisocyanate (HDI). Two or more polyisocyanates may beused in combination. In light of the weather resistance, TMXDI, XDI,HDI, H₆XDI, IPDI and H₁₂MDI are preferred.

As also noted herein, it has been discovered that as the melt index of apolymer increases, some of the physical properties of the polymerdecrease. As a result, in the more preferred embodiments of theinvention the high melt index golf ball components are further treatedwith a liquid isocyanate solution. By performing an isocyanatepost-molding treatment process to the golf ball, the physical propertiesof the thermoplastic polyurethane, polyurea or polyurethane/polyureacover material may not only increase, but may increase beyond the valuesof the non-refined material. This physical property improvement yields asignificant improvement in golf ball durability, namely improved cut andscuff (groove shear) resistance.

This post-application of isocyanate is believed to allow for the use ofrelatively high melt index thermoplastic polyurethane, polyurea orpolyurethanes/polyureas to be used in conventional injection moldingmachines and/or in reaction injection molding (“RIM”) equipment to moldthin wall layers, i.e. 0.075 inches, more preferably 0.050 inches andbelow, preferably 0.040 inches and below, more preferably 0.030 inchesand below, and most preferably 0.025 inches and below. The moldedthin-walled golf balls are preferably dipped in an isocyanate solutionfor 1 to 10 minutes (preferably 1 to 5 minutes); the isocyanate may bealiphatic or aromatic, such as HDI, IPDI, MDI, TDI type or others asdiscussed below and the isocyanate solution may range from 10 to 100%solids. The solvent used to reduce the solids and make the isocyanatesolutions may be a ketone or acetate or any solvent that will allowpenetration of the isocyanate into the cover material without distortingthe cover. After dipping, the balls are air-dried for 1 hour and thenpost-cured at 175° F. for 4 hours. After the post-cure the balls may becleaned with isopropanol to remove any excess isocyanate from the coverand the balls are then finished in a normal manner. Preferably, theisocyanate used is of the MDI type at 15-30% solids reduced with aketone (such as Mondur ML™ from Bayer Corporation) and dipped for 2-3minutes. Most preferably, the solids level is about 16 to 24%(20.+−0.4). It is beneficial that the MDI remain in a liquid state atroom temperature. However, this method shall not be limited to the typeof polyurethane, polyurea or polyurethane/polyurea material, isocyanateused, concentration of the isocyanate solution, solvent used, dip time,or method of application described above.

Isocyanate Indexing:

In some embodiments, the cross-linking may take place as a result of therelative proportions of isocyanate functional groups in the cover layerand the coating layer. As is generally known, polyurethanes (whetherthermoplastic or thermoset) are polymerized through the reaction betweenan isocyanate functional group on a polyisocyanate and a hydroxylfunctional group on a polyol. The relative stoichiometric amounts ofeach of these functional groups is expressed as the “isocyanate index”of the polyurethane system. Namely, the isocyanate index may beexpressed as the ratio of the number of isocyanate groups present in thepolyurethane system to the number of hydroxyl groups times 100. Or, inother words, the isocyanate index may be expressed as the ratio of theactual number of isocyanate functional groups present in thepolyurethane system to the hypothetical number of isocyanate functionalgroups necessary to fully react with all of the hydroxyl groups presentin the polyurethane system.

The isocyanate index may also be referred to as the “NCO index.” Thelocation of the decimal place may vary based on common convention (i.e.the value of the isocyanate index may be equally expressed as 1.00 or100 depending on colloquialism). As used herein, an isocyanate indexvalue of 100 means that the number of isocyanate functional groupspresent in the polyurethane system is equal to the number of hydroxylfunctional groups present in the polyurethane system. An isocyanateindex value of less than 100 means that excess hydroxyl groups arepresent, and an isocyanate index value of greater than 100 means thatexcess isocyanate groups are present.

In certain embodiments, the isocyanate index of the coating layer may bedifferent from the isocyanate index of the cover layer. Particularly,the isocyanate index of the coating layer may differ from 100 by a firstcertain amount, the isocyanate index of the cover layer may differentfrom 100 by a second certain amount, where one of the isocyanate indexvalues is above 100 and the other is below 100. More specifically, theisocyanate index of the coating layer may be at least a firstpredetermine amount above 100, while the isocyanate index of the coverlayer may be at least a second predetermine amount below 100. The firstpredetermined amount and the second predetermined amount may be the sameor different. In other embodiments, the isocyanate index of the coatinglayer may be at least a first predetermine amount below 100, while theisocyanate index of the cover layer may be at least a secondpredetermined amount above 100.

It should be understood that the different embodiments for coating thegolf balls as described above are for illustrative purposes only and notmeant to be restrictive. Other embodiments include, for example, aprocess where the molded TPU golf ball is first sprayed with apolyurethane primer further containing an excess of isocyanate(over-indexed) by at least 105 or more, and more preferably by 110 ormore. After drying (evaporation of solvent) and cure of both the PUprimer and at least a portion of the TPU outermost skin, a second stepof applying a PU topcoat is performed. A preferred means of drying andcuring in all golf ball coating embodiments is via Infrared heat.

In a second example, the molded TPU golf ball is first sprayed with apolyurethane primer further containing an excess of isocyanate(over-indexed) by at least 105 or more, and more preferably by 110 ormore. After drying (evaporation of solvent) and cure of both the PUprimer and at least a portion of the TPU outermost skin, a second stepof applying a PU topcoat which is under-indexed occurs. The polyol richPU topcoat will react with any unreacted Isocyanate leftover from theover-indexed prime-coat. The topcoat is under-indexed to 98 or less, andpreferably 95 or less.

In a third example, the molded TPU golf ball is first sprayed with asimple solution of isocyanate in a solvent. After an appropriatedrying/reacting time and temperature, a PU prime coat (which may or maynot be over-indexed) is applied followed by the application of a PUtop-coat (which may or may not be under-indexed).

In a fourth example, the molded TPU golf ball is first sprayed asdescribed above in Examples 1, 2, or 3, except that a reaction enhancingcatalyst is added to any coating. Such a catalyst promoted the reactionof isocyanate and TPU and also ensures reaction of nearly all,preferably all, of the excess isocyanate present in the golf ball coverand/or coating layers. The catalyst may comprise at least one memberselected from the group consisting of dibutyl tin dilaurate, dibutyl tinacetylacetonate, dibutyl tin dibutoxide, dibutyl tin sulphide, dibutyltin di-2-ethylhexanoate, dibutyl tin (IV) diacetate, dialkyltin (IV)oxide, tributyl tin laurylmercaptate, dibutyl tin dichloride, organolead, tetrabutyl titanate, tertiary amines, mercaptides, stannousoctoate, potassium octoate, zinc octoate, diaza compounds, and potassiumacetate.

Prior to the application of any coating it may be desirable to heat thegolf ball to enhance/improve the ability of the isocyanate in thecoating to react with the TPU. Infrared (IR) heat may be an ideal way toquickly warm the cover layer. A warm coating may also improve thereaction/reaction rate.

Prior to spraying the golf ball with any coating any number ofpre-treatments may be used to effect greater/higher degree ofcross-linking between the isocyanate and TPU such as: a) spray/dippingthe TPU ball with solvent only; b) corona or plasma treatment of the TPUball; c) adding catalyst to the TPU composition; d) addingisocyanate/isocyanate masterbatch to the TPU composition; e) addingantioxidant/antiozonant, HALS, UV absorber, and the like to the TPUcomposition or any TPU coating layer; f) under-indexing the TPUcomposition to a polyol rich index to provide more sites for subsequentreaction with the isocyanate; g) adding unsaturated reactive sites tothe TPU (e.g., diene) for free-radical crosslinking that wouldultimately combine a variety of crosslinks to the TPU cover. Such meansof free radical crosslinking would be radiation (gamma, e-beam) or if aperoxide or other initiator is added to the TPU in bulk or via solutiontreatment, heat could then be used to cross-link the composition.

Thickness and Hardness of Golf Balls

The golf balls of this invention provide the ball with a variety ofadvantageous mechanical and playing performance properties as discussedfurther below. In general, the hardness, diameter, and thickness of thedifferent ball layers may vary depending upon the desired ballconstruction. If the ball includes an intermediate layer or inner coverlayer, the hardness (material) is about 50 Shore D or greater, morepreferably about 55 Shore D or greater, and most preferably about 60Shore D or greater. In one embodiment, the inner cover has a Shore Dhardness of about 62 to about 90 Shore D. In one example, the innercover has a hardness of about 68 Shore D or greater. In addition, thethickness of the inner cover layer is preferably about 0.015 inches toabout 0.100 inches, more preferably about 0.020 inches to about 0.080inches, and most preferably about 0.030 inches to about 0.050 inches.

The outer cover preferably has a thickness within a range having a lowerlimit of about 0.004 or 0.010 or 0.020 or 0.030 or 0.040 inches and anupper limit of about 0.050 or 0.055 or 0.065 or 0.070 or 0.080 inches.Preferably, the thickness of the outer cover is about 0.020 inches orless. The outer cover preferably has a surface hardness of 65 Shore D orless, or 55 Shore D or less, or 50 Shore D or less, or 50 Shore D orless, or 45 Shore D or less. Preferably, the outer cover has hardness inthe range of about 20 to about 59 Shore D. In one example, the outercover has hardness in the range of about 25 to about 55 Shore D.

The method of this invention is particularly effective in providing golfballs having a thin outer cover layer. Furthermore, the method of thisinvention provides thin outer covers with substantially uniformthickness. The resulting balls of this invention have good impactdurability and cut/shear-resistance. The United States Golf Association(“USGA”) has set total weight limits for golf balls. Particularly, theUSGA has established a maximum weight of 45.93 g (1.62 ounces) for golfballs. There is no lower weight limit. In addition, the USGA requiresthat golf balls used in competition have a diameter of at least 1.68inches. There is no upper limit so many golf balls have an overalldiameter falling within the range of about 1.68 to about 1.80 inches.The golf ball diameter is preferably about 1.68 to 1.74 inches, morepreferably about 1.68 to 1.70 inches. In accordance with the presentinvention, the weight, diameter, and thickness of the core and coverlayers may be adjusted, as needed, so the ball meets USGA specificationsof a maximum weight of 1.62 ounces and a minimum diameter of at least1.68 inches.

Preferably, the golf ball has a Coefficient of Restitution (COR) of atleast 0.750 and more preferably at least 0.800 (as measured per the testmethods below.) The core of the golf ball generally has a compression inthe range of about 30 to about 130 and more preferably in the range ofabout 70 to about 110 (as measured per the test methods below.) Theseproperties allow players to generate greater ball velocity off the teeand achieve greater distance with their drives. At the same time, therelatively thin outer cover layer means that a player will have a morecomfortable and natural feeling when striking the ball with a club. Theball is more playable and its flight path can be controlled more easily.This control allows the player to make better approach shots near thegreen. Furthermore, the outer covers of this invention have good impactdurability and mechanical strength.

Referring to FIG. 1, a front view of a finished golf ball that can bemade in accordance with this invention is generally indicated at (10).The dimples (12) may have various shapes and be arranged in variouspatterns to modify the aerodynamic properties of the ball.

As shown in FIG. 2, a two-piece golf ball (14) can be made having a core(16) and a surrounding thermoplastic polyurethane outer cover layer(18). In the golf ball (14), the core (16) has a relatively largediameter and the outer cover (18) has a relatively small thickness.Referring to FIG. 3, in another embodiment, a two-piece golf ball (20)having a smaller core (22) and a thicker outer cover layer (24) can bemade. Turning to FIG. 4, a three-piece golf ball (26) is made, whereinthe dual-layered core (inner core (28) and outer core layer (30) issurrounded by a single-layered thermoplastic polyurethane cover (32).

In FIG. 5, a partial cut-away view of a three-piece golf ball (42)having an inner core (44), outer core (46) and surrounding thermoplasticpolyurethane cover (48) is shown. Finally, in FIG. 6, a four-piece ball(50) containing a dual-core having an inner core (52) and outer corelayer (54) is shown. The dual-core is surrounded by a multi-layeredcover with an inner cover layer (56) and thermoplastic polyurethaneouter cover (60).

It should be understood that the golf balls shown in FIGS. 1-6 are forillustrative purposes only, and they are not meant to be restrictive.Other golf ball constructions can be made in accordance with thisinvention.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball sub-assembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore C or Shore Dor Shore A hardness) was measured according to the test method ASTMD-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core×amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball sub-assembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

It is understood that the manufacturing methods, compositions,constructions, and products described and illustrated herein representonly some embodiments of the invention. It is appreciated by thoseskilled in the art that various changes and additions can be made tocompositions, constructions, and products without departing from thespirit and scope of this invention. It is intended that all suchembodiments be covered by the appended claims.

We claim:
 1. A coated golf ball formed by a method, the methodcomprising the steps of: providing a golf ball comprising at least onecore layer and an outer cover layer, wherein the outer cover layer isformed from a thermoplastic polyurethane composition; applying a mixturecomprising multi-functional isocyanate and solvent to the outer coverlayer; applying a first polyurethane coating comprising unreactedisocyanate groups and having an isocyanate index of at least about 115to the outer cover layer; treating the golf ball with heat; and applyinga second polyurethane coating to the outer cover of the golf ball toform a coated golf ball.
 2. The golf ball of claim 1, wherein theisocyanate is selected from the group consisting of 4,4′-methylenediphenyl diisocyanate (MDI), 2,4′-methylene diphenyl diisocyanate (MDI),toluene 2,4-diisocyanate (TDI), toluene 2,6-diisocyanate (TDI),4,4′-dicyclohexylmethane diisocyanate (H₁₂ MDI), p-phenylenediisocyanate (PPDI), and isophorone diisocyanate (IPDI), andhomopolymers and copolymers and blends thereof.
 3. The golf ball ofclaim 1, wherein the solvent is selected from the group consisting ofketones, acetates, and mixtures thereof.
 4. The golf ball of claim 1,wherein the mixture further comprises an ultraviolet (UV) lightstabilizer.
 5. The golf ball of claim 1, wherein at least one of thefirst and second polyurethane coatings further comprises a catalyst. 6.The golf ball of claim 1, wherein the thermoplastic polyurethanecomposition further comprises a catalyst.
 7. The golf ball of claim 6,wherein the catalyst is selected from the group consisting of dibutyltin dilaurate, dibutyl tin acetylacetonate, dibutyl tin dibutoxide,dibutyl tin sulphide, dibutyl tin di-2-ethylhexanoate, dibutyl tin (IV)diacetate, dialkyltin (IV) oxide, tributyl tin laurylmercaptate, dibutyltin dichloride, organo lead, tetrabutyl titanate, tertiary amines,mercaptides, stannous octoate, potassium octoate, zinc octoate, diazocompounds, and potassium acetate, and mixtures.